Rockwell Automation AutoMax Enhanced Ladder Editor - Manual (Page 77)

CĆ1
Appendix C
Using the PreĆDefined (Reserved) Ladder
Language Variables
The Editor contains preĆdefined variables that you can use in an individual
ladder program to:
D execute logic based on a Processor scan
D specify how to handle error conditions
D check scan time execution
The preĆdefined ladder language variables are local variables, which you can
use for ladder instruction parameters. Their names are reserved and appear in
the choices offered by the Variable Smart Matching option.
Using the PreĆDefined Program Scan Variables
Use the following Boolean variables to execute logic based on the Processor's
scan. Only use these variables for input parameters (readĆonly):
D first_scan Use this variable to execute logic during a program's
first scan. This variable is true during the initial scan
of the ladder rung and false during all other scans.
D second_scan Use this variable to execute logic during a program's
second scan. This variable is true during the second
scan of the ladder rung and false during all others.
D last_scan Use this variable to execute logic during a program's
last scan. This variable is true on the final pass of the
ladder rung after you have selected TASK STOP. This
variable is not set when a STOP ALL error occurs.
To use the last_scan variable, your program scan
must be less than 0.5 seconds.
I
MPORTANT
Do not use the last_scan variable in an eventĆdriven
program. Because these programs are based on the
occurrence of an event, the last_scan variable may
never be executed when used in an eventĆdriven
program.